1. Technical Field
This invention relates generally to digital video signal compression, and more particularly to methods of three-dimensional digital video signal compression that exhibit a high compression ratio, minimal signal distortion and a low transmission rate.
2. Discussion
Present video applications require large amounts of data to be transmitted at high bit rates and with a minimal amount of signal distortion. For example, the uncompressed data bit rates for monochrome digital video, such as VCR-grade v-deo (SIF), broadcast television video (CCIR-601) and high definition television (HDTV) are 16 Mbps, 67 Mbps, and 240 Mbps, respectively. In an uncompressed state, these data bit rates are too high to allow such video signals to be transmitted and processed in a commercially feasible manner. Therefore, in order to process such video signals in a practical manner, such video signals must be compressed prior to being transmitted.
In response to the proliferation of video based applications and products, an industry wide need for creation of a standard video signal compression syntax arose. A group under the International Standards Organization (ISO), known informally as the Moving Pictures Experts croup (MPEG), was formed to define standards for digital video and audio compression. Subsequently, the MPEG has created a standardized syntax by defining the content of a compressed video signal bit stream and the method of decompressing the bit stream subsequent to its transmission. The methods of compression, however, have not been defined, thus allowing individual manufacturers to develop various methods of actually compressing the data bit stream within the defined standards.
MPEG has to date defined two syntaxes widely used in the digital videos industry. A syntax known as MPEG-1 was defined to be applicable to a wide range of bit rates and sample rates. Particularly, MPEG-1 is suitable for use in CD/ROM applications and other non-interlaced video applications having transmission rates of about 1.5 Mb/s. A second syntax known as MPEG-2 was defined for representation of broadcast video, and other video signal applications having coded bit rates of between 4 and 9 Mb/s. MPEG-2 syntax is also applicable to applications such as HDTV and other applications requiring efficient coding of interlaced video.
While the above discussed MPEG-1 and MPEG-2 syntaxes exhibit adequate performance characteristics, the ongoing evolution of digital video dictates the need for further advancement in the art, as the present MPEG video syntax definitions do have associated limitations. For example, temporal redundancy, a phenomenon which can be used to enhance video compression by minimizing data bit rate Transmission for temporarily non-changing video pixels, is an efficient method of maximizing video signal compression. Present MPEG-1 and 2 data compression-based methods utilize temporal compression. However, the MPEG-1 and 2-based temporal compression is based on a frame by frame judgment basis so that the methods do not take full advantage of temporal compression. In particular, commercially standard MPEG-1 and MPEG-2 syntaxes partially only utilize temporal redundancy. In addition, present MPEG syntax requires numerous optimization options (such as predictive frame, bi-linear frame and intraframe variables) to be calculated, transmitted and then decoded by MPEG signal aggressors. The use of these numerous variables adds both computational time and complexity to the data compression. Also, while many current MPEG implemented syntaxes exhibit an associated bit rate compression of as high as 30:1, increasingly complex and data-intensive video applications require higher compression rates for real-time processing. Although data compression methods claiming compression ratios as high as 200:1 do exist, such methods subsample an array of pixels in a video frame sequence (i.e., throw away every other pixel) and utilize other shortcuts to achieve high compression.
With the ever increasing need to achieve higher bit rate transmission, there is a need for a video signal data compression method that exhibits a lower transmission rate than present MPEG-1 or MPEG-2 standards by achieving a higher compression ratio through more complete utilization of temporal redundancy than is presently utilized by MPEG 1 and 2-based standards. At the same time there is a need for a data compression method that is less computationally complex than current methods and that is compatible with currently implemented video systems conforming to MPEG-1 and MPEG-2 standards.